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 TM 55-1905-219-14-4
3-12. BLOWER - MAINTENANCE INSTRUCTIONS
a. General.
(1) The blower supplies fresh air for combustion and scavenging to the diesel engine. Two hollow
three-lobe rotors revolve with very close clearances in a housing bolted to the top deck of the cylinder block,
between two banks of cylinders. The rotor lobes are made with a helical (spiral) form to provide continuous and
uniform displacement of air.
(2) The blower has a 2.05:1 ratio blower-to-engine speed. Two timing gears on the drive end of the
rotor shafts space the rotor lobes with a close tolerance. As the lobes of the two rotors do not touch at any
time, no lubrication is required.
(3) Lip type oil seals are installed in the blower end plates. Each rotor is supported in the doweled
end plates of the blower housing by a roller bearing at the front end and a two row pre-loaded radial and thrust
ball bearing at the gear end. The right-hand helix rotor of the blower is driven at approximately twice engine
speed by the blower drive shaft. The blower drive shaft is splined at one end to a flexible drive hub attached to
the blower drive gear and at the other end to a flexible coupling attached to the right-hand helix blower timing
gear. The mating left-hand helix timing gear drives the left-hand helix rotor.
(4) The flexible coupling, formed by an eliptical cam driven by two bundles of leaf springs which ride
on four semi-cylindrical supports, is attached to the blower right-hand helix timing gear and prevents the
transfer of torque fluctuations to the blower.
(5) The blower rotors are timed by two rotor gears at the rear end of the rotor shafts. This timing must
be correct, or the required clearance, obtained by the use of shims behind the gears, and between the rotor
lobes will not be maintained.
(6) Normal gear wear causes a decrease of rotor-to-rotor clearance between the leading edge of the
right-hand helix (drive) rotor and the trailing edge of the left-hand helix (driven) rotor. Clearance between the
opposite sides of the rotor lobes is increased correspondingly.
(7) While the rotor lobe clearance may be corrected by adjustment, gear backlash cannot be
corrected. When gears have worn to the point where the backlash exceeds .004 inch (0.01 cm), replace the
gears. Refer to DIRECT SUPPORT MAINTENANCE.
3-476
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